The 11-year-old girl with leukemia and a heart catheter, whom authorities call just Emily, could die in a matter of days if she is not brought back to an Arizona hospital after her parents inexplicably took her out of the facility last week, authorities said Monday.

Phoenix police are asking anyone with information about their whereabouts to come forward.

We just don't know what their intent was. But this could become extremely serious if she contracts an infection.

- Phoenix police Sgt. Steve Martos

Authorities said the little girl had been receiving chemotherapy at Phoenix Children's Hospital for about a month, said Phoenix police Sgt. Steve Martos.

An infection forced doctors to amputate her right arm and insert a catheter in her heart. The device was set to be taken out before her mother removed an IV from the girl, changed her clothes, and walked her out of the hospital Wednesday night.

Police said if the catheter is left in too long, it could lead to a deadly infection.

"If she contracts an infection, it really could just be a matter of days that could result in the young girl's death," Martos said. "It's pretty serious."

Authorities had been stymied by health privacy laws that kept them from releasing the parents' names, but late Monday police said U.S. Border Patrol stopped the girl's father, Luis Bracamontes, 46, as he crossed into Arizona from México over the weekend.

Martos said the man provided no clues of the girl's whereabouts and denied having any involvement in removing her from the hospital. Police are now releasing his name, along with the mother, Norma Bracamontes, 35, in hopes it will help locate the child.

"We believe he has had some contact with her over the weekend and possibly even the night she was released," Martos said on Tuesday on America's Newsroom on Fox News Channel. "It seems a bit odd to us that a father would not know where his sick daughter would be."

Neither parent is charged with a crime yet, but authorities want the child brought back to the hospital before it's too late, Martos said.

He said the family lives a "nomadic" life without a permanent residence, but they have relatives in Arizona, California and México, none of whom have been able to provide police with information about their whereabouts.

The girl's father is a Mexican citizen with a green card. The child and her mother are U.S. citizens, according to Martos.

Authorities don't know why the child's parents took her from the hospital, but speculate they might have been concerned with paying the bill.

Surveillance footage from Wednesday night shows the mother pushing an IV stand through a hospital hallway. The young girl with her right arm removed above the elbow and wrapped in a bandage is seen walking beside her.

"We just don't know what their intent was," Martos said. "But this could become extremely serious if she contracts an infection ... Our primary concern is that she gets the proper medical care so we can prevent obviously the worst-case scenario here."